Interval notation is a method for writing intervals on a number line. Solutions can be written using brackets and parentheses.

 

For < and > use (     )

For     use [    ]  

Always use a (  ) with Infinity

 

 
 

For example, how would you write the following inequality?

x > 3

Always write from left to right.

There is a greater than sign so use a parenthesis and it goes to infinity so use a parenthesis sign.

( 3, ∞ )

 

Let’s look at another example.

 x ≤ 2

Remember, you read from left to right.

There is a less than and equal to sign so it goes to infinity on the left, and then a 2 and it is less than and equal to so it will have brackets.

( ∞, 2 ]

 

 

 

 

 
 

In summary, interval notation is a method for writing inequalities using paranthesis and brackets. Parenthesis are used with less than and greater than plus infiniti and brackets are used with greater than and equal to plus less than and equal to.